Technics SA-DA20 Operating Instructions Manual page 14

< Customizing your receiver
For front speakers with an impedance under 6 n
Turn "LOW IMP" on if even one of your speakers has an impedance
under 6 O.
Press and hold [A] or [B] until "LOW IMP"
lights up on the display.
Press and hold down again to cancel "LOW IMP".
Note that when "LOW IMP" is on, SPEAKERS A and B cannot be
used at the same time.